With feature sizes in very large scale integration (VLSI) shrinking well below the micron level, reduction in resistivity of conducting layers throughout the integrated structure has become increasingly important. One particular layer that has been incorporated in gate stacks of transistors in, for example, static random access memory (SRAM) cells and dynamic random access memory (DRAM) cells is a refractory metal silicide, such as tungsten silicide (WSi.sub.x). Such refractory metal silicides are effective to reduce the sheet resistance of the doped polysilicon layer that is incorporated in the gate, since the metal silicides have a lower resistivity than the polysilicon layer. While silicides of titanium (Ti), tungsten (W), tantalum (Ta), molybdenum (Mo), cobalt (Co), etc. have been utilized, nitrides of such refractory metals may also be utilized.
Because the refractory metal silicide is generally formed directly on the polysilicon layer of the gate stack, a pre-clean step is usually carried out to improve adhesion between the deposited material and the polysilicon layer and to reduce particle count (thus decreasing defectivity) at the interface. For example, the polysilicon may be pre-cleaned with an HF treatment, followed by rinsing with isopropol alcohol. The pre-clean step is generally considered effective to remove the native oxide that forms on the polysilicon, as well as any screen oxide thereon. However, the present inventors have recognized a need in the art to improve further the yield of such devices. Particularly, the present inventors have focused on defectivity caused by particles present at the interface between the deposited conductive layer and the polysilicon layer.